Demineralization of water is often carried out using service demineralizers which employ the principle of either mixed bed or separate bed demineralization. The water is rendered mineral free, selectively or entirely, by passing it through a bed or filter of completely mixed ion-exchange materials (mixed bed) or through separate beds of individual ion exchange materials (separate beds) contained in the service demineralizers.
The ion exchange resins are of two types, namely cation exchange resin in hydrogen ion form and anion exchange resin in hydroxyl ion form. The cation exchange resin removes cations, typically calcium, magnesium, sodium, potassium, iron and manganese from the water, while the anion exchange resin removes anions, typically carbonates, bicarbonates, sulfates, chlorides, nitrates and silica. An efficient mixed-bed ion exchanger is able to produce water of high purity by removal of the ionic species.
The ion exchange resins become exhausted in use but may be regenerated for reuse. In the case of the anion exchange resin, regeneration may be effected using sodium hydroxide solution, while hydrochloric acid may be used to regenerate the cation exchange resin. The service demineralizer often takes the form of a portable exchange cylinder which, when exhausted, is removed and replaced by a fresh cylinder. The exhausted cylinder is returned to a central regeneration plant. One such plant has been described in Canadian Pat. No. 856,301 and its equivalent U.S. Pat. No. 3,429,807. Exhausted ion exchange material from more than one service unit, which may be mixed bed or separate bed, is regenerated simultaneously in the plant.
In the latter procedure, following removal of impurities from the ion exchange material, anion exchange resin and cation exchange resin are placed in separate regeneration vessels. When mixed bed material is processed, the resins are hydraulically separated prior to transfer to their respective regeneration vessels. The resins are regenerated simultaneously by passing a caustic solution through the exhausted anion exchange resin and an acid solution through the exhausted cation exchange resin. Following regeneration, the ion exchange resins are rinsed with demineralized water. The regenerated resin then is transferred to the service unit, following hydraulic mixing of the resin types for a mixed bed unit.
This prior art procedure is labour intensive and prone to operator error. The procedure is also very inefficient with respect to energy utilization and water utilization. Nevertheless there are a large number of plants in the United States and Canada which utilize this prior art procedure for lack of a better procedure.